Electric power systems rely mainly on fossil fuels to cover the electricity demand, since electricity generation from fossil fuels is a proven, reliable technology and the electrical output from steam and gas turbine generators is regulated. However, fossil fuels are exhaustible, costly, and cause environmental problems, such as the emission of gases to the atmosphere. In a number of countries there are alternative methods of electricity generation that are equally reliable, such as hydro and biomass electricity generation or nuclear generation. However, not all countries have these natural resources and/or the adequate technology to develop this type of power plants.
There is a trend in developing new methods of electricity generation, mainly from renewable sources, such as wind and solar energy. These forms of renewable energy cannot be harnessed effectively due to a number of problems, such as the variability of wind and solar radiation, the need to use expensive inverters to transform direct current (DC) electricity to alternating current (AC) electricity, low efficiencies of photovoltaic panels, and the insertion of harmonics into the power grid [Z. Chen and E. Spooner, “Grid power quality with variable speed wind turbines,” IEEE Trans. on Energy Conversion, vol. 16, no. 2, June 2001, pp. 148-154], [F. D. Kanellos and N. D. Hatziargyriou, “The effect of variable-speed wind turbines on the operation of weak distribution networks,” IEEE Trans. on Energy Conversion, vol. 17, no. 4, December 2002, pp. 543-548], [R. L. Scragg and A. B. Parker, “Electrical power generation and storage system,” U.S. Pat. No. 4,084,038, April 1978], [A. J. Goldman, “Electrical energy system,” U.S. Pat. No. 5,121,044, June 1992], [W. Cooper, “Renewable energy electric power generating system,” U.S. Pat. No. 7,233,079, June 2007].
The proposed method uses a connection of equipment, machines and technologies in a novel configuration, as explained below. The method is able to alleviate the operating problems of the aforementioned renewable sources and offer a reliable way of harvesting renewable energy. The proposed method is also able to feed the renewable energy into the electricity network, in synchronism with the traditional (e.g. fossil fuel) generators of the system. The proposed method can compete economically with the conventional methods and provide a stable, reliable and financially sound environmental alternative to electricity generation. The electromechanical system proposed, using a combination of a DC motor and an AC generator, replaces the expensive inverter that is currently used and that creates problems with harmonic voltages/currents in the network. The proposed method enables the development of renewable power plants of much higher rating, since the cost and size prohibitions of inverters, as well as their power quality problems, would no longer be an issue. Further, with this method there is no longer a need of elaborate control mechanisms to control the frequency of the electricity output of wind turbines, as the wind turbines will be used for the production of hydrogen and will not be connected directly to the grid.
There is a continuing need for harvesting renewable energy without endangering the stability of the grid and the continuity of the supply.